Conventionally, soft plastic such as polyvinyl chloride, polyethylene, etc. has been adopted as thermoplastic resin constituting a tube. However, a fluoro resin has been adopted in view of improving the barrier capacity and the chemical resistance (refer to Japanese Patent Laid-open Publications 2000-43286, HEI09-131833, and 2003-80724, for instance). The fluoro resin has a good barrier capacity and a good chemical resistance, in particular, a high steam barrier performance and a relatively high oxygen barrier performance, however, it is difficult to produce a flexible tube, since it is generally rigid and has a high melting point. Such being the case, the steam barrier performance is worsened in a case where the flexibility of the tube is sought, while on the other hand, the flexibility of the tube is worsened in a case where the steam barrier performance is sought. This means that there is a technical problem of incompatibility between the steam barrier performance and the flexibility of the tube.
Japanese Patent Laid-open Publication 2000-43286 discloses a tube suitable for an ink supply tube of an ink jet printer comprising PCTFE copolymer as a fluoro component which is formed by the copolymerization of a fluoro resin with a soft component and a thermoplastic resin such as ECTFE (ethylene-chlorotrifluoroethylene) to exhibit a low extension coefficient.
However, in a case where the copolymer of the fluoro resin is used, it is necessary to increase the thickness of the barrier resin layer in order to obtain a tube including a desired barrier capacity, since the barrier capacity of the resin itself is decreased. This causes a technical problem of a decrease of the transparency and the kink resistance, since it is not possible to set an outer diameter of the tube itself to be small.
In addition, each of the Japanese Patent Laid-open Publications HEI09-131833 and 2003-80724 discloses a multi-layer tube constituted by laminating a fluoro resin layer, and a soft rubber or an elastomer layer. This multi-layer tube was attempted to be applied to a wide range of technical fields by laminating a fluoro resin layer which includes a good steam barrier performance and a chemical stability, and the soft rubber or the elastomer layer, however, there is a technical disadvantage that this tube is not suitable for co-extrusion forming because of a low adhesiveness between these two resins. Various improvements have been made to solve this disadvantage.
The Japanese Patent Laid-open Publication HEI09-131833 discloses a multi-layer tube which comprises a thermoplastic elastomer (a1), a fluoro resin (b1) and an intermediate adhesive layer between the thermoplastic elastomer (a1) and the fluoro resin (b1) which is constituted by a polymer alloy in which a thermoplastic polymer including adhesive properties to the elastomer layer and a resin including fluorine having adhesive properties to the fluoro resin layer are dispersed in such a way that the thermoplastic polymer and the resin constitute a sea-island pattern, and which multi-layer tube is produced by forming the thermoplastic elastomer (a1), the fluoro resin (b1) and the intermediate adhesive layer in a co-extrusion manner.
However, although the adhesive properties can be improved by adopting such polymer alloy, this tube has a poor transparency, since fluoro resin is dispersed in the thermoplastic polymer, and since it is necessary to adjust an amount of the resin constituting the adhesive layer, in view of attaining the desired flexibility and kink resistance of this tube, this tube has an unstableness in that its adhesive strength can be varied even by a slight difference of the ratio of components of this tube.
The Japanese Patent Laid-open Publication 2003-80724 discloses an ink tube consisting of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) resin layer and a silicon rubber layer. However, the fluoro resin consisting of FEP has a high melting point so that it is technically difficult to form this tube with an elastomer in a co-extrusion manner, and since FEP has a poor adhesive properties with the silicon rubber layer, it is necessary to treat a surface of FEP in order to laminate it with the silicon rubber layer, etc.